Laser-induced crystallization of monoclinic nanowires in glassy selenium films

The authors investigate influence of 632.8 nm laser irradiation on structural properties of thin glassy (amorphous) Se films synthesized on quartz substrates using vacuum thermal evaporation. They first propose the fact that low power laser irradiation of Se films (power density PS=80 W cm−2) initiates phase transformations, accompanied by growth of monocrystalline nanowires of metastable phase of monoclinic beta-Se8 in the amorphous matrix at room temperature. New structural properties of Se films are proven to be long term stable at room temperature. It is shown that laser irradiation at PS ≥ 800 W cm−2 induces synthesis of a mixture of nanocrystallites of trigonal Se and monoclinic alpha-Se8 in the amorphous films and their mass crystallization with growth of spherulites at room temperature

Photon-drag in single-walled carbon nanotube and silver-palladium films

Polarization influence on the photovoltaic current raised due to the photon-drag effect in the single-walled carbon nanotube (SWNT) films and nanostructured silver-palladium (Ag/Pd) resistive films is examined at the wavelengths of 532 and 1064 nm of nanosecond laser pulses. The SWNT films were synthesized by the aerosol chemical vapor deposition technique. Ag/Pd films, consisting of AgPd alloy and palladium oxide (PdO), were prepared by burning a special paste on a ceramic substrate. The films obtained were characterized by Raman spectroscopy. It is shown that the Ag/Pd films Raman spectra consist of PdO peak that moves from 650 cm-1 to 628 cm-1 as the excitation He-Ne laser power increases. The photocurrent was measured at the oblique incidence of the laser beam on the film in the direction perpendicular to the plane of incidence. It is found that the transverse photocurrent in the SWNT films at circular polarization is absent and does not depend on the direction of the electric field vector rotation (the sign of the circular polarization) of the incident irradiation. The photocurrent in the Ag/Pd films at circular polarized irradiation is significant and depends on the circular polarization sign. The results obtained demonstrate the potential applications of the Ag/Pd resistive films as a sensor of the circular polarization sign of the incident light pulse in a wide wavelength range.Peer reviewe

Femtosecond Circular Photon Drag Effect in the Ag

We report on the observation of the helicity-dependent photoresponse of the 20-μm-thick silver–palladium (Ag p - and s -polarized beams, while its sign is opposite for the right- and left-circularly polarized beams. By comparing experimental results with theoretical analysis, we show that the photoresponse of the A

Incident Angle Dependence of the Waveform of the Polarization-Sensitive Photoresponse in CuSe/Se Thin Film

The results of studying the waveforms of longitudinal and transverse photocurrent pulses generated in thin, semitransparent CuSe/Se films as a function of the angle of incidence (α) of a femtosecond laser beam at linear and circular polarizations are presented. It has been established that the durations of unipolar longitudinal photocurrent pulses at linear and circular polarizations of laser pumping do not depend on the angle α. It is shown that the evolution of the temporal profile of the helicity-sensitive transverse photocurrent with a change in α strongly depends on polarization. At linear polarization, the shape of the unipolar pulses remains virtually constant; however, at circular polarization, the generation of unipolar and bipolar pulses is possible, with the waveforms strongly depending on the angle α. The influence of the incidence angle on the waveforms of transverse photocurrent pulses is explained by the transformation of linear and circular polarization into an elliptical upon the refraction of light at the air/semitransparent film interface and by the interplay of photocurrents arising due to linear and circular surface photogalvanic effects in the film. The presented findings can be utilized to develop polarization and incidence angle-sensitive photovoltaic devices

Low-Power Laser Graphitization of High Pressure—High Temperature Nanodiamond Films

Laser-induced graphitization of 100 nm monocrystals of diamond particles synthesized by high-pressure high-temperature (HP-HT) methods is not typically observed. The current study demonstrates the graphitization of 150 nm HP-HT nanodiamond particles in ca. 20-μm-thick thin films formed on a glass substrate when the intensity of a focused 633 nm He-Ne laser exceeds a threshold of ~ 33 kW/cm2. Graphitization is accompanied by green luminescence. The structure and morphology of the samples were investigated before and after laser excitation while using X-ray diffraction (XRD), Raman spectroscopy, atomic force (AFM), and scanning electron microscopy (SEM). These observations are explained by photoionization of [Ni-N]- and [N]-centers, leading to the excitation of electrons to the conduction band of the HP-HT nanodiamond films and an increase of the local temperature of the sample, causing the transformation of sp3 HP-HT nanodiamonds to sp2-carbon

The Surface Photogalvanic and Photon Drag Effects in Ag/Pd Metal-Semiconductor Nanocomposite

We performed the investigation of the polarization-sensitive photocurrent generated in silver-palladium metal-semiconductor nanocomposite films under irradiation with nanosecond laser pulses at the wavelength of 2600 nm. It is shown that in both the transverse and the longitudinal configuration, the surface photogalvanic (SPGE) and photon drag effects (PDE) contribute to the observed photocurrent. However, the temporal profile of the transverse photocurrent pulse is monopolar at any polarization and angle of incidence, while the temporal profile of the longitudinal photocurrent pulse depends on the polarization of the excitation beam. Specifically, the irradiation of the film with the s-polarized excitation beam produces a monopolar photoresponse, while at p-polarized excitation, the photoresponse is bipolar, having a short front and long tail. Obtained experimental results are in agreement with the developed phenomenological theory, which describes transverse and longitudinal photocurrents due to SPGE and PDE in terms of relevant second-order nonlinear susceptibilities and allows us to obtain their dependences on the angle of incidence and polarization of the excitation laser beam. The pronounced dependence of the photocurrent on the angle of incidence and polarization of the excitation beam opens avenues toward the development of polarization- and position-sensitive detectors for industrial and space applications

Heat-Induced Dip of Optical Limiting Threshold in Carbon Nanotube Aqueous Suspension

Carbon nanotube (CNT) suspensions possess nonlinear light scattering, which leads to a manifestation of the optical limiting (OL) phenomenon. Here we present the results of research into the temperature influence on the OL of multiwalled CNT suspensions. The experiments were carried out with a stable aqueous suspension of chemically treated CNTs synthesized by graphite arc evaporation. The OL study was performed by a z-scan technique using a 532 nm single-mode nanosecond laser. An increase in the suspension temperature by 17 °C from 23 to 40 °C was found to result in 3 times reduction of the OL threshold intensity of the suspension. Upon further heating, the OL threshold remains constant. The analysis of the results obtained is presented. Our experimental findings allow one to reveal the optimal temperature range for an optical limiter based on aqueous CNT suspension